(PHP 8 >= 8.2.0)
sodium_crypto_stream_xchacha20_xor_ic — Encrypts a message using a nonce and a secret key (no authentication)
$message,$nonce,$counter,$keyThe function is similar to sodium_crypto_stream_xchacha20_xor() but adds the ability to set the initial value of the block counter to a non-zero value. This permits direct access to any block without having to compute the previous ones.
This encryption is unauthenticated, and does not prevent chosen-ciphertext attacks. Make sure to combine the ciphertext with a Message Authentication Code, for example with sodium_crypto_aead_xchacha20poly1305_ietf_encrypt() function, or sodium_crypto_auth().
messageThe message to encrypt.
nonce24-byte nonce.
counterThe initial value of the block counter.
keyKey, possibly generated from sodium_crypto_stream_xchacha20_keygen().
Encrypted message, or false on failure.
Example #1 sodium_crypto_stream_xchacha20_xor_ic() example
<?php
$n2 = random_bytes(SODIUM_CRYPTO_STREAM_XCHACHA20_NONCEBYTES);
$left = str_repeat("\x01", 64);
$right = str_repeat("\xfe", 64);
// All at once:
$stream7_unified = sodium_crypto_stream_xchacha20_xor($left . $right, $n2, $key);
// Piecewise, with initial counter:
$stream7_left = sodium_crypto_stream_xchacha20_xor_ic($left, $n2, 0, $key);
$stream7_right = sodium_crypto_stream_xchacha20_xor_ic($right, $n2, 1, $key);
$stream7_concat = $stream7_left . $stream7_right;
var_dump(strlen($stream7_concat));
var_dump($stream7_unified === $stream7_concat);
?>The above example will output something similar to:
int(128) bool(true)